if you tell your doctor you are not sexually active at a physical, does that mean they don't test for std's?

They normally do not test for STDs during a routine physical unless you mention any symptoms

Typically, doctors will take you at your word, and they can't force you to submit to testing. They also don't run tests unless they think you need them. If you are displaying symptoms that are indicative of an STD, they will encourage you to run the test, even if you tell them you're not sexually active, just to rule it out.

If you tell your doctor you're not sexually active, that means you have never had sex before.
If you haven't had sex before (including oral sex and anal sex) and if you don't share needles, or put your self at risk by exchange blood or body fluids with infected people then there's no reason to test you for stds.
Also doctors don't test you for stds during a routine physicals, or with routine blood work unless you speak to them about it or mention your symptoms.